U.S. Pat. No. 3,992,099 to Laughlin, incorporated herein by reference, discloses a source discriminator for measuring the angle of arrival and wavelength of beams of radiant energy. Such a system is useful in combat applications as a threat warning system to provide information about the source of ranging laser beams and the like. The source discriminator described in the Laughlin patent includes first and second planar radiant energy detectors transversely oriented relative to one another to receive radiant energy. Each of the detectors produces an electrical output signal corresponding to radiant energy which impinges on the detector. The output signals are used to determine the angle of arrival and wavelength of the radiant energy impinging upon the planar detectors. The detectors have an angular response approximated by the cosine function.
However, it has been found that many radiant energy beams, such as laser beams, to be detected by the device are non-homogeneous and have hot spots, or varying optical gradients, across the cross-section of the beam. This non-homogeneity of the beam adversely affects the accuracy of prior detector systems. An additional problem arises from a passivating overcoat layer typically included on the surface of prior planar detectors used in systems such as disclosed in the Laughlin U.S. Pat. No. 3,992,099. The passivating overcoat layer acts as a transmission line whose characteristics vary as a function of both the wavelength and the polarization of radiant energy impinging upon the passivating overcoat surface. Variations caused by the passivating overcoat thus adversely affect the accuracy of results determined by prior detecting systems. It has also been found that reflections and shadowing from the detector mounting and detector electrode post used with prior systems can adversely affect the accuracy of the system.
A need has thus arisen for an improved radiant beam discriminator which minimizes or eliminates the effects of non-homogeneous radiant energy beams, and which reduces inaccuracies caused by passivating overcoats or mounting reflections and shadowing.